MIPS: Add CP0 macros for extended EntryLo registers

Add read/write macros to access the upper bits of the
extended EntryLo0 and EntryLo1 registers used by XPA.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8455/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>